The present invention relates to an engine, which is for vehicles (e.g., automobiles), and for directly injecting fuel containing gasoline into cylinders and performing compression self-ignition combustion (CI combustion), and it particularly relates to an art for utilizing ozone.
CI combustion is a combustion mode in which self-ignition of mixture gas containing gasoline is caused by compressing the mixture gas within cylinders to increase a temperature and pressure thereof. Unlike a conventional combustion mode (spark ignition) in which the mixture gas is ignited by spark ignition, and the flame produced thereby propagates to cause combustion, with the CI combustion, the mixture gas ignites at various positions within each cylinder simultaneously. Since the CI combustion has a shorter combustion period compared to the spark ignition, lower fuel consumption and lower NOx production can be expected.
On the other hand, the CI combustion has a disadvantage that an operating range for the CI combustion to be performed stably is narrow. Therefore, to stimulate the CI combustion, an ignition assist for inducing a plurality of simultaneous ignitions by performing the spark ignition within a predetermined operating range is performed. For example, JP2012-241590A discloses such an art. However, to perform such an ignition assist, installation and control of an ignition plug are required.
Moreover, as another method of stimulating the CI combustion, ozone application is utilized. By suitably mixing ozone with the mixture gas within the cylinder, the self-ignition can be induced and, thus, the CI combustion especially at a low temperature can be expected to be stimulated. Such stimulation of the CI combustion by ozone is disclosed in JP2002-309941A.
With the engine in JP2002-309941A, ozone is generated by an ozone generating device and is supplied into the cylinder. Specifically, the fuel and ozone are supplied into the cylinder during compression stroke so that the ozone can be well mixed with the mixture gas while being efficiently supplied into the cylinder.
Although a detailed configuration of the ozone generating device is not disclosed in JP2002-309941A, a silent electric discharging method using dielectric barrier electric discharge is generally used in ozone generating mechanisms of conventional ozone generating devices.
FIG. 1 is a view illustrating a basic structure of a main part (cell 100) of an ozone generating device which adopts such a silent electric discharging method. The cell 100 is comprised of a pair of electrodes 101 connected with a high-frequency high-voltage power source, and a dielectric body 102 having electric insulation properties, such as glass.
The pair of electrodes 101 are disposed to face each other via a gap, and the dielectric body 102 is attached to one or both (in FIG. 1, both) of the opposing surfaces of the electrodes 101. According to the shape of the electrodes 101, the cell 100 is formed into a plate or a tube, for example.
In generating ozone, a pulse-shaped high voltage is applied between both of the electrodes 101 so that electricity is discharged in the gap between the electrodes 101, and material gas containing oxygen, such as air, is supplied to the gap where the electricity is discharged. In this manner, ozone is generated by the material gas passing through the gap. The applied voltage is generally about a few kV to a few 10 kV with a pulse width of about a few μs to a few 10 μs (microseconds).
The dielectric bodies 102 prevent a high current from flowing between the electrodes 101 so that a spark or heat is not generated between the electrodes 101 by a high voltage application. However, a voltage loss is caused by the dielectric bodies 102, and thus the silent electric discharging method has disadvantages in terms of ozone generation efficiency and energy utilization efficiency.
In generating ozone with the ozone generating device as above, in addition to the disadvantages in ozone generation efficiency and energy utilization efficiency, if the ozone is supplied into the cylinder from the ozone generating device, ozone will be reduced and the energy will be lost also during the supplying process.
Therefore, engines in which ozone generated by an ozone generating device is supplied into cylinders have disadvantages in terms of ozone generation efficiency and energy utilization efficiency. Moreover, since the ozone needs to be suitably mixed with intake air and the supply of ozone requires time, a disadvantage in terms of responsiveness in control also rises.
To reduce such disadvantages, with the engine in JP2002-309941A, ozone is supplied into the cylinder during the compression stroke; however, since ozone is a gas, it needs to be pressured by a higher pressure than the in-cylinder pressure before being supplied, and the device structure and the control thereof inevitably become complicated.